The evolution of P/F vs T/K raises important questions

[Mauro]

Again, in my recollection the left context of p/f (distribution of letters that can precede p/f) is rather similar to that of k/t; but the right context is different from that of k/t -- but somewhat more like that of ke/te.  Which seems consistent with your observation of the increased frequency of "ch" there.

All the best, --stolfi

I like the terms 'left' and 'right context'! Caveat first: 'p' is a relatively rare glyph, and 'f' even more so, I can't vouch about the soundness of statistics on those glyphs, expecially 'f'.

Anyway: p/f and k/t do indeed seem to be paired, at least in Herbal A: the left context distance between p and f is 0.08 and the right context distance is 0.15 (for k/t: 0.07 and 0.12; for reference ch/sh are 0.23 and 0.08), rather small. But between k and p (the most frequent glyphs of the two groups) the left-context distance is 0.22, the right-context one is 0.34 (between t and p: 0.28 and 0.25).

Edit. One thing I did not notice previously: 'e' and 'ckh' are quite close as right-context, distance = 0.1 (which is rather surprising to me). Very far as left-context though (0.63).